Re: [PATCH 1/9] seek_sanity_test: fix allocation unit detection on XFS realtime

["liuyd.fnst@fujitsu.com" <liuyd.fnst@fujitsu.com>]

Hi, guys.

Recently I hit a regression during test xfstest. Reverting this commit 
could fix that error.

Reproduce steps (only nfs4.2 has this error):
```
# cat local.config

export TEST_DEV=127.0.0.1:/home/nfs/share0

export TEST_DIR=/mnt/test

export SCRATCH_DEV=127.0.0.1:/home/nfs/share1

export SCRATCH_MNT=/mnt/scratch

export FSX_AVOID="-E"

export NFS_MOUNT_OPTIONS="-o rw,relatime,vers=4.2"


# ./check -nfs generic/285

FSTYP         -- nfs

PLATFORM      -- Linux/aarch64 hpe-apollo80-01-n00 
5.14.0-131.el9.aarch64 #1 SMP PREEMPT_DYNAMIC Mon Jul 18 16:13:44 EDT 2022

MKFS_OPTIONS  -- 127.0.0.1:/home/nfs/share1

MOUNT_OPTIONS -- -o rw,relatime,vers=4.2 -o 
context=system_u:object_r:root_t:s0 127.0.0.1:/home/nfs/share1 /mnt/scratch



generic/285 2s ... [failed, exit status 1]- output mismatch (see 
/root/xfstests/results//generic/285.out.bad)

     --- tests/generic/285.out	2022-07-27 21:07:43.160268552 -0400

     +++ /root/xfstests/results//generic/285.out.bad	2022-07-27 
21:31:27.887090532 -0400

     @@ -1 +1,3 @@

      QA output created by 285

     +seek sanity check failed!

     +(see /root/xfstests/results//generic/285.full for details)

     ...

     (Run 'diff -u /root/xfstests/tests/generic/285.out 
/root/xfstests/results//generic/285.out.bad'  to see the entire diff)

Ran: generic/285

Failures: generic/285

Failed 1 of 1 tests


```

Reverting this commit then test pass.
```
# git revert e861a30255c9780425ee5193325d30882fbe7410
# make -j && make install -j
---snip---
# ./check -nfs generic/285

FSTYP         -- nfs

PLATFORM      -- Linux/aarch64 hpe-apollo80-01-n00 
5.14.0-131.el9.aarch64 #1 SMP PREEMPT_DYNAMIC Mon Jul 18 16:13:44 EDT 2022

MKFS_OPTIONS  -- 127.0.0.1:/home/nfs/share1

MOUNT_OPTIONS -- -o rw,relatime,vers=4.2 -o 
context=system_u:object_r:root_t:s0 127.0.0.1:/home/nfs/share1 /mnt/scratch



generic/285 1s ...  1s

Ran: generic/285

Passed all 1 tests

```

On 6/29/22 04:21, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> The seek sanity test tries to figure out a file space allocation unit by
> calling stat and then using an iterative SEEK_DATA method to try to
> detect a smaller blocksize based on SEEK_DATA's consultation of the
> filesystem's internal block mapping.  This was put in (AFAICT) because
> XFS' stat implementation returns max(filesystem blocksize, PAGESIZE) for
> most regular files.
> 
> Unfortunately, for a realtime file with an extent size larger than a
> single filesystem block this doesn't work at all because block mappings
> still work at filesystem block granularity, but allocation units do not.
> To fix this, detect the specific case where st_blksize != PAGE_SIZE and
> trust the fstat results.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>   src/seek_sanity_test.c |   12 +++++++++++-
>   1 file changed, 11 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/src/seek_sanity_test.c b/src/seek_sanity_test.c
> index 76587b7f..1030d0c5 100644
> --- a/src/seek_sanity_test.c
> +++ b/src/seek_sanity_test.c
> @@ -45,6 +45,7 @@ static int get_io_sizes(int fd)
>   	off_t pos = 0, offset = 1;
>   	struct stat buf;
>   	int shift, ret;
> +	int pagesz = sysconf(_SC_PAGE_SIZE);
>   
>   	ret = fstat(fd, &buf);
>   	if (ret) {
> @@ -53,8 +54,16 @@ static int get_io_sizes(int fd)
>   		return ret;
>   	}
>   
> -	/* st_blksize is typically also the allocation size */
> +	/*
> +	 * st_blksize is typically also the allocation size.  However, XFS
> +	 * rounds this up to the page size, so if the stat blocksize is exactly
> +	 * one page, use this iterative algorithm to see if SEEK_DATA will hint
> +	 * at a more precise answer based on the filesystem's (pre)allocation
> +	 * decisions.
> +	 */
>   	alloc_size = buf.st_blksize;
> +	if (alloc_size != pagesz)
> +		goto done;
>   
>   	/* try to discover the actual alloc size */
>   	while (pos == 0 && offset < alloc_size) {
> @@ -80,6 +89,7 @@ static int get_io_sizes(int fd)
>   	if (!shift)
>   		offset += pos ? 0 : 1;
>   	alloc_size = offset;
> +done:
>   	fprintf(stdout, "Allocation size: %ld\n", alloc_size);
>   	return 0;
>   
>